In general, loudness of a sound (sound pressure) produced by a sounding body is dependent on the displacement of a vibrating part, which is the sound source of the sounding body, under conditions in which the surface area of the vibrating part and the frequency are unchanged. Thus, conventionally, a typical method used for obtaining a desired sound pressure includes inputting an analog signal to the sounding body and vibrating the sounding body in accordance with the amplitude of the analog signal. Vibrating the sounding body with analog signals causes a lower S/N ratio under the influence of switching noise, sampling error, or the like. Thus with the objective of increasing the S/N ratio and broadening dynamic range, digital speakers are disclosed in which piezoelectric elements are directly driven in accordance with digital signals without involving conversion from digital signals to analog signals (see Patent Literatures 1 and 2, for example). In the piezoelectric speaker disclosed in Patent Literature 1, piezoelectric layered structures are arranged in parallel on a vibrating plate (a substrate), where the number of layers in each structure varies with the weight of the corresponding bit in bit string data. In the PCM acoustic converter disclosed in Patent Literature 2, piezoelectric layered structures are stacked in the layering direction, where the number of layers in each structure varies with the weight of the corresponding bit in the bit string data.